PCBM exhibits excellent interfacial compatibility with perovskite, facilitating the fabrication of high-performance devices. Its remarkable electron transfer capacity allows for efficient electron extraction from the perovskite layer, and the molecules readily aggregate into large clusters, reducing the interfacial area required for electron dissociation. However, PCBM's relatively low ionization potential leads to severe charge recombination. Furthermore, its lowest unoccupied molecular orbital (LUMO) is not optimally aligned with the perovskite work function, thus reducing device performance.

To address these challenges, the teams of Professors Li Xiong of Huazhong University of Science and Technology and Zang Zhigang of Chongqing University achieved more uniform PCBM films by incorporating tetramethylthiourea (TMDS). The TMDS-modified PCBM exhibits a uniform surface morphology with little aggregation, ensuring complete PCBM coverage of the perovskite layer. Under UV light, TMDS readily forms highly active reducing organic radicals in solution, facilitating the doping of the classic electron acceptor PCBM.

Ultimately, the target device achieved a top-performing PCE of 26.10% (certified at 25.39%), while a 1cm² device achieved a PCE of 24.06%. Under simulated AM1.5 illumination, the target device maintained above 95% of its initial efficiency after 1271 hours of continuous maximum power point tracking (MPPT). After aging for 1090 hours at 85°C and 85% relative humidity (RH), the encapsulated target device maintained above 90% of its initial PCE. TMDS-modified PCBM exhibited excellent performance in PSCs, significantly improving electron extraction to significantly suppress charge recombination efficiency, while also exhibiting superior stability compared to conventional PSCs. This research is of great significance for improving the performance and stability of inverted perovskite solar cells and will help promote the industrialization of perovskite solar cells.

Fig. 1 | N doping effect and interactions. a PSCs structure and schematic illustration of chemical interactions between perovskite and TMDS or sulfur radicals.b Formation of sulfur radicals and n doping mechanism of PCBM. c Time-of-flight mass spectrum of PCBM with TMDS film. d The ESR spectra of different solutions.e XPS spectra of S 2p for TMDS and PCBM films without and with TMDS. XPS spectra of (f)S2p and (g) Pb 4 f, for TMDS and PVSK films without and with TMDS.h FTIR spectra of TMDS and PVSK films without and with TMDS.

Fig. 3 | Passivation and carrier transport. a Energy level diagram of the PCBM films without and with modifiers as well as perovskite film. b, c GIWAXS mappings of the perovskite films with and without TMDS treatment. d SCLC plots of the electron-only device ITO/SnO2/perovskite/PCBM/Ag where the PCBM films without and with TMDS were used. e, f PL mapping images of glass/perovskite without and with TMDS. g, h PL mapping images of the glass/perovskite/PCBM without and with TMDS. i PL and (j) TRPL spectra of the glass/perovskite without and with TMDS. k PL and (l) TRPL spectra of the glass/perovskite/PCBM without and with TMDS.